I moved my DS at 21 months after a long list of concerns, and he settled their immediately. He had been at first nursery for 9 months and still hadn't settled there. IME it's down to the new one having staff who give a damn, who like their jobs and who love being with children in a hands on way. They get down to their level and play and stimulate them, he has fun now, whereas the old one was fab facilities, massive countryside site, but high staff turnover, mainly young staff, who all just stood around the edge of the room gossiping rather than playing with the children etc. listen to your gut.
We moved at 21 months as we moved house (80 miles) so had to move her out of necessity. I was tricky for a few weeks (tears on drop off) and she was also a bit naughty in general hitting other kids- but I put that down to just there being a massive change and upheaval in her life. It all ony lasted a few weeks. Children are v good at adjusting you will be fine!
Actually I have a similar dilemma at the moment, as we don't really like her current nursery and ideally we would like to change but now she is very settled (and the nursery is v convenient location wise). Tricky to know what to do. For the moment we are just going to sit tight as expecting DD # 2 any day now so doesn't seem sensible to move DD 1 who is now 2 years 10 months - it would be too much upheaval at once.
I'd say trust your instincts... If you're not happy and you've found a nicer place then I'd move her.