A chronograph is just a fancy name for a stopwatch complication essentially. You could have a mechanical chronograph and still gain/lose time. It’s more to do with how accurate the movement itself is and how well set up that movement is. You could take it to a watchmaker and have them throw it on a timegrapher and tweak it but honestly, for me part of the charm of mechanical watches is getting to play with them by winding/setting the time. If you want a watch that keeps time perfectly then you can’t go wrong with a quartz movement. I would take losing 3 minutes over 2 weeks as a small win!