Vegas Pro 15 was released nearly 7 years ago. The best way to improve it is to upgrade to Vegas Pro 21 or wait a while until Vegas Pro 22 is released (already previewed in https://www.vegascreativesoftware.info/us/forum/2-for-1-deal--146325/#ca918379 ). If you bought Vegas Pro 15 from MAGIX or one of its licensed distributors (but not Steam), you may be eligible for upgrade pricing which will be less than the 2-for-1 offer.
The only caveat is that you will need a modern computer that meets the specifications for current day Vegas Pro versions. A trial version of Vegas Pro 21 is available from Vegas Pro 21's product webpage.
@Tadeusz-Ostrowski As you've posted on the VEGAS Movie Studio subforum, so not sure if you actually have one of the VMS 15 versions. Anyway, if the conditions @Dexcon mentioned are met, you should be eligible for the current 2-for-1 upgrade pricing as well.