As someone who makes signatures, 70 kb is way too small. If you think it isn't too small, you've never dealt with making signatures fit the size limit. It's honestly such a hassle, and I have to often settle for lower quality images than what I make in PS.
Don't get me this "I don't want large pictures eating my data" crap... It's 2021. Almost everyone has an unlimited data plan, and if you don't, loading 150kb images up from 70kb isn't going to make much of a difference. Any streaming content or non-optimized website is going to eat far more than a CONTROLLED increase in allowed size for signatures. It's 150KB, not 5MB, calm down, throw away your iPhone 4 and your Cricket Wireless prepaid minutes plan and join us in 2021.