Is it common for a fund to ask to talk to our previous investors?

That is exceptionally common. Your previous (early) investors are the people are the most hyped up, aside from the founders, presumably. Those investors have seen you grow to $63k in MRR, and are about to see great IRR when you do a priced round. They should be doubling down on your narrative to investors, whether it’s founder/marketing fit, strong growth, or FOMO. Make sure you prep them with a phone call in regards to this.