Is it possible to upgrade from the select electronic edition to Komplete 15 Standard edition?
I am rather sure that that is possible since Kpmplete Select Electronic edition appears to me as part of a new type of Select bundles that represents the new line of Entry Level bundle(s) replacing the previous unified type entry level product , but try logging into the N.I. Site on the account where you have the select then click the Komplete 15 Standard edition buy link or this link to same then click the upgrade and there should appear a text telling if you are qualified. Other wise then if any further doubt then you can contact N.I. Purchase Support and get confirmation. Otherwise then if you buy something directly from N.I. shop that does not fit the account it were bought for then I think that usually there would not be a problem getting a refund (as long as that you do not redeem and download the product).
P.S. you can see full list of content and prices at the compare page.