In order to reduce the amount of power adapters, I would like to use an apple 96W USB-C power adapter on an old MacBook Pro Retina 15" from mid 2014, with an adapter cable USB-C to MagSafe. Is this possible? Are there any downsides, like too much power which results in faster loading which in turn produces more heat which in turn decreases battery lifespan?
As far as I know, Apple sells only a USB-C to MagSafe 3 cable - not one for MagSafe 2. However, there are other companies who make and sell USB-C to MagSafe 2 adapters. Those would be third party ofcourse.
In terms of having a 96W USB-C adapter instead of for example the 87W or 61W USB-C adapter - that's not a problem. It is not so that the charger "pushes" 96W of power into the device causing it to overheat and destroy the battery. Instead the computer determines how large wattage it draws.