You will be able to convert the installation that you have to either the creative cloud subscription plan or to the Lightroom 6 standalone plan. The conversion will take place to what you have installed, so everything that you have done including creating presets will remain in place. The presets are part of the catalog, which is a user-created file that isn't replaced anyway when newer versions are installed.
Yes, those presets will still be there when you will buy the product.
Lightroom 6/CC are compatible with Windows 10 though there are few differences between CC2015 and standalone version 6 like dehaze is not there in version 6.