If you are looking to download and install Real Cricket 15 on your desktop, you can find the software on Cnet. I don't find Real Cricket 15 as an app, but as a software program that can be downloaded and installed on a Windows PC desktop or laptop.
However, if you'd like to download and install Real Cricket 18, you can find this on the Google Play store for Android devices.
I did find one download for Real Cricket 15, but this seems to only be for a Windows phone and not all Android devices. I would go with Real Cricket 18 and you should be fine.