Walked around my property for 1 mile at an avg pace of 2.5 mph according to my watch. heart rate got up to 115 bpm. is that too fast for simple walking? there is an ever so slight uphill elevation to start and then it's back down hill after that?

HR of 115 with that mild to moderate exercise is reasonable, but it should return to your baseline (hopefully 60-80 beats/min within 2-3 minutes of stopping the exercise, & should not be accompanied by chest pain/pressure or excessive shortness of breath.

I, and you, need to know the temperature, the wind speed, the humidity and calories burned to be able to figure this out. You also need a table for folks your age, gender and perhaps ethnicity average heart rate for this amount of exercise with the amount af energy you expend. Send more details.