Be careful you aren't loading the entire font family.
If I load "Chalkboard SE" it will take 4-6 seconds, and appear to work.
But if I load ChalkboardSE-Regular , it's virtually instantaneous ~100ms or less.
Here's a list of the actual font names you should use:
AcademyEngravedLetPlain
AlNile-Bold
AlNile
AmericanTypewriter-Light
AmericanTypewriter-CondensedLight
AmericanTypewriter-CondensedBold
AmericanTypewriter
AmericanTypewriter-Condensed
AmericanTypewriter-Bold
AppleColorEmoji
AppleSDGothicNeo-Thin
AppleSDGothicNeo-UltraLight
AppleSDGothicNeo-SemiBold
AppleSDGothicNeo-Medium
AppleSDGothicNeo-Regular
AppleSDGothicNeo-Bold
AppleSDGothicNeo-Light
ArialMT
Arial-BoldItalicMT
Arial-ItalicMT
Arial-BoldMT
ArialHebrew-Bold
ArialHebrew-Light
ArialHebrew
ArialRoundedMTBold
Avenir-Heavy
Avenir-Oblique
Avenir-Black
Avenir-Book
Avenir-BlackOblique
Avenir-HeavyOblique
Avenir-Light
Avenir-MediumOblique
Avenir-Medium
Avenir-LightOblique
Avenir-Roman
Avenir-BookOblique
AvenirNext-MediumItalic
AvenirNext-Bold
AvenirNext-UltraLight
AvenirNext-DemiBold
AvenirNext-HeavyItalic
AvenirNext-Heavy
AvenirNext-Medium
AvenirNext-Italic
AvenirNext-UltraLightItalic
AvenirNext-BoldItalic
AvenirNext-Regular
AvenirNext-DemiBoldItalic
AvenirNextCondensed-Regular
AvenirNextCondensed-MediumItalic
AvenirNextCondensed-UltraLightItalic
AvenirNextCondensed-UltraLight
AvenirNextCondensed-BoldItalic
AvenirNextCondensed-Italic
AvenirNextCondensed-Medium
AvenirNextCondensed-HeavyItalic
AvenirNextCondensed-Heavy
AvenirNextCondensed-DemiBoldItalic
AvenirNextCondensed-DemiBold
AvenirNextCondensed-Bold
BanglaSangamMN
BanglaSangamMN-Bold
Baskerville-Bold
Baskerville-SemiBoldItalic
Baskerville-BoldItalic
Baskerville
Baskerville-SemiBold
Baskerville-Italic
BodoniSvtyTwoITCTT-Book
BodoniSvtyTwoITCTT-Bold
BodoniSvtyTwoITCTT-BookIta
BodoniSvtyTwoOSITCTT-BookIt
BodoniSvtyTwoOSITCTT-Bold
BodoniSvtyTwoOSITCTT-Book
BodoniSvtyTwoSCITCTT-Book
BodoniOrnamentsITCTT
BradleyHandITCTT-Bold
ChalkboardSE-Light
ChalkboardSE-Regular
ChalkboardSE-Bold
Chalkduster
Cochin-Bold
Cochin-BoldItalic
Cochin-Italic
Cochin
Copperplate
Copperplate-Light
Copperplate-Bold
Courier
Courier-Oblique
Courier-BoldOblique
Courier-Bold
CourierNewPSMT
CourierNewPS-BoldMT
CourierNewPS-ItalicMT
CourierNewPS-BoldItalicMT
DamascusBold
Damascus
DamascusLight
DamascusMedium
DamascusSemiBold
DevanagariSangamMN
DevanagariSangamMN-Bold
Didot-Bold
Didot-Italic
Didot
DINAlternate-Bold
DINCondensed-Bold
EuphemiaUCAS
EuphemiaUCAS-Bold
EuphemiaUCAS-Italic
Farah
Futura-Medium
Futura-CondensedMedium
Futura-MediumItalic
Futura-CondensedExtraBold
GeezaPro-Bold
GeezaPro
Georgia-BoldItalic
Georgia-Bold
Georgia-Italic
Georgia
GillSans
GillSans-Italic
GillSans-BoldItalic
GillSans-Light
GillSans-LightItalic
GillSans-Bold
GujaratiSangamMN-Bold
GujaratiSangamMN
GurmukhiMN-Bold
GurmukhiMN
STHeitiSC-Medium
STHeitiSC-Light
STHeitiTC-Medium
STHeitiTC-Light
Helvetica-Oblique
Helvetica-Light
Helvetica-Bold
Helvetica
Helvetica-BoldOblique
Helvetica-LightOblique
HelveticaNeue-BoldItalic
HelveticaNeue-Light
HelveticaNeue-Italic
HelveticaNeue-UltraLightItalic
HelveticaNeue-CondensedBold
HelveticaNeue-MediumItalic
HelveticaNeue-Thin
HelveticaNeue-Medium
HelveticaNeue-ThinItalic
HelveticaNeue-LightItalic
HelveticaNeue-UltraLight
HelveticaNeue-Bold
HelveticaNeue
HelveticaNeue-CondensedBlack
HiraKakuProN-W6
HiraKakuProN-W3
HiraMinProN-W6
HiraMinProN-W3
HoeflerText-Regular
HoeflerText-BlackItalic
HoeflerText-Italic
HoeflerText-Black
IowanOldStyle-Bold
IowanOldStyle-BoldItalic
IowanOldStyle-Italic
IowanOldStyle-Roman
Kailasa
Kailasa-Bold
KannadaSangamMN
KannadaSangamMN-Bold
KhmerSangamMN
KohinoorDevanagari-Light
KohinoorDevanagari-Book
KohinoorDevanagari-Medium
LaoSangamMN
MalayalamSangamMN
MalayalamSangamMN-Bold
Marion-Regular
Marion-Italic
Marion-Bold
MarkerFelt-Thin
MarkerFelt-Wide
Menlo-BoldItalic
Menlo-Regular
Menlo-Bold
Menlo-Italic
DiwanMishafi
Noteworthy-Bold
Noteworthy-Light
Optima-Regular
Optima-Italic
Optima-Bold
Optima-BoldItalic
Optima-ExtraBlack
OriyaSangamMN
OriyaSangamMN-Bold
Palatino-Roman
Palatino-Italic
Palatino-Bold
Palatino-BoldItalic
Papyrus-Condensed
Papyrus
PartyLetPlain
SavoyeLetPlain
SinhalaSangamMN
SinhalaSangamMN-Bold
SnellRoundhand-Black
SnellRoundhand-Bold
SnellRoundhand
Superclarendon-Regular
Superclarendon-BoldItalic
Superclarendon-Light
Superclarendon-BlackItalic
Superclarendon-Italic
Superclarendon-LightItalic
Superclarendon-Bold
Superclarendon-Black
Symbol
TamilSangamMN
TamilSangamMN-Bold
TeluguSangamMN
TeluguSangamMN-Bold
Thonburi-Bold
Thonburi
Thonburi-Light
TimesNewRomanPS-BoldItalicMT
TimesNewRomanPSMT
TimesNewRomanPS-BoldMT
TimesNewRomanPS-ItalicMT
Trebuchet-BoldItalic
TrebuchetMS
TrebuchetMS-Bold
TrebuchetMS-Italic
Verdana-BoldItalic
Verdana-Italic
Verdana
Verdana-Bold
ZapfDingbatsITC
Zapfino
See https://gilesey.wordpress.com/2015/01/14/ios-spritekit-font-loading-times-of-sklabelnodes/