Should I change my flight? (connecting in LHR)

HI there! please forgive my ignorance. My husband, daughter, and I will be traveling to/from India this summer. our last trip there was in 2018, when we lived in NYC, and could take direct flights. This is our first international trip where we have to make a transfer, and I think I may have made in a mistake by booking a return trip that doesn't have sufficient travel time. Currently, we are scheduled to fly on British Airways, Mumbai to DFW, transferring at London Heathrow. We are supposed to leave at 9am on Monday, June 16th, land at LHR in terminal 5 at 2:40 pm, and then our next flight leaves out of terminal 3 at 4:25 pm. That's 1 hour and 45 minutes to make the next flight. Is this cutting it too close? I could rebook our flights to leave Mumbai at 1:40 am, get to LHR and have a 3 hour layover--this option is much more expensive ($500-$800 more), which is why I want to be absolutely sure that I make the right choice. Can anyone offer insight/advice?