If you mean that the nuclear reactors consume fuel slower (assuming 120 UPS, less power per tick but the same fuel per second) and the heat exchangers consume the heat in balance, and the steam turbines consume the steam in balance as well.
Can you give an specific example of what the rates are normally, what they are with GTTS enabled, and what you think they should be with GTTS enabled?
So when it says 15 MW, it means 15 MJ per 60 ticks. That is 0.25 MJ per tick, and 40MJ per 160 ticks, so 40 MJ per second or an actual 40MW. The reported rates are based on the base game speed of 60 ticks per second, and I can't change that. Any build will produce power at 2.666 times the rate that is reported, and any building will consume power at 2.666 times the rate reported.
The power consumption of all other buildings should be reduced by the same ratio. A factory that uses 120KW normally should be reduced to 45KW with GTTS enabled to be in balance.
It should not matter what the target UPS is. There could be some oddities in the heat transfer or fluid transfer dynamics due to the UPS change, but those should be in your benefit at 160UPS.
If you still think it's a problem, could you post a screenshot of both the power production and consumption with GTTS set to 160 UPS, and also set GTTS to 60 UPS wait a while for everything to stabilize with the new rate and show another screenshot of the power production and consumption? If there is some power consumer or producer that is not being adjusted in balance, it should show up there.