This might be a very easy thing but still
For example:
The price rises from $2500 to $3000, this in an increase of 1.15%.
So should I do 1.15*(the bitcoin amount I have now at the price of 2500) ?
Use a portfolio, or an exchange. For your question though, you would do
3000-2500= 500
2500/500 = 5 = 1/5 = 20% profit
I don't know where you got 1.15 from?
1.15*2500 = 2875$