@Bily_jednorozec Thank you so much Bily! I'm so glad this was able to help you!
@ZeeGee I have over 800 patterns, actually. I converted them all to .package file. I'll try to answer your questions.
Categories that have a lot of patterns in them, or even have a lot of re-colorations of EA patterns saved, will take a minute or two to load. For me, Fabric and Themed categories have the most patterns, so these take a couple of minutes to finish loading. Wood I have a lot of also, so it takes about a minute. However, my Misc category has maybe 20 patterns, but TONS of individual color saves of default patterns... and so it -also- takes a bit to load. Basically the lag or loading time of a category depends not on the patterns themselves but on how many thumbnails the game needs to load. I've actually tried to cut back on saving a re-color of a pattern to the pattern category for that reason.
My patterns are all merged together with CC magic, and they work just fine. Bily's question was about merging a pattern together with an object, which I couldn't answer because I haven't tried putting patterns in the same merge package as an object, but merging all the patterns themselves together is definitely not a problem.