Yeah, texture uploads are slow. Text does not do anything specific to handle this, but often text objects do not change every frame, so they just render like sprites and largely get away with it. Large text objects that change text every tick have been reported to be slow before, but there's not much to be done about it, so we just advise to avoid that case if possible, or use SpriteFonts which render directly without any texture uploads.
Since a Spine animation presumably can be expected to always change contents every frame, then it will hit you harder. There's very little that can be done to optimise it, other than not using texture uploads at all. That is why my very first suggestion was to find a way to render it directly, so this problem would be bypassed. The main advantage of using texture uploads is that it's probably much quicker to get it working, since you mentioned it looked difficult to set up the library to render directly... so to completely solve this, you're probably just going to have to bite the bullet and do all that work.