Aside from CQRS as suggested by others, would a simple Lazy loading be a good solution to this problem? Order items will not be loaded if they are not accessed. Or a dedicated OrderSummary/OrderStatus domain object if you can not use lazy loading?
Also it is always worth reconsidering whether a heavy aggregate is really needed. There may simply be no domain rules that call for it. Life cycle for example is a well known 'wrong reason' for having heavy aggregates (like Group->User, or Product->BacklogItem). Highly recommended read on this subject: Aggregate design.