Minimum charger brick wattage allowed for new 14" MacBook Pro?

Curious to find out the minimum allowed charging requirements for the newest 14" MacBook Pro M1 Pro chip base model... 8-Core, 14-Core GPU, 16GB Unified Memory, and 512GB SSD. It came with the 87W charging brick, and I was also told it is compatible to use the 96W charger for the fast charging feature.

However, my question is that I have a 61W charging brick w/ USB-C at my moms for convenience when I visit over there from my 2019 MacBook Pro that I had. Will I be able to continue using the 61W charging brick using USB-C, or should I invest in the larger size? They're not exactly cheap so just trying to figure out if it's worth the investment and if I need to toss the 61W brick... and I don't need it for fast charging when I stay plugged in 90% of the time anyways. Just don't want to harm the system by using a lower wattage charger if that is bad for the system, and I can't seem to find any information on whether it would be safe to use with my new 14" MacBook Pro...