Greetings, it would be better to keep the sprouts as it is with 15 trillion sprouts. At this point in time there is nothing to be gained by making the supply lower, we might as well just keep it as is, that way it stays fair for early investors. Also, who knows what could happen to the price even with 15 trillion. I mean these are not dollars were talkin' here.
It seems a lot of people have not noticed, with the Hard Fork in 2018 it was not only the staking reward that was reduced, but a coin burn method was built in which slowly reduces the total supply of Sprouts at no cost to the hodlers of SPRTS.
You can have a look at the block explorer at
https://chainz.cryptoid.info/sprts/#@inflation. For a better view click "Last 100k blocks". As you can then see SPRTS is not inflating, but deflating.