Alot depends on how many addons you have installed. Theres several videos on youtube about sizing down "Bloatware" and deleting Thumbnail files etc...
Search Google and Youtube for some advice.
maybe the t1 does not have enough memory to play 4k video, by looking at the specs it seems like the t1 would have a hard time with 4k, don't own one so can't test but do use H96 pro+ with 3g/32 for memory and can play 4k smoothly through kodi