Is there a way to install OpenJDK 15 in Ubuntu bionic?

I would like to use newest Java (15) and I can't find it in ubuntu bionic repositories. Is there a ppa where I could get it?

Yes, you can get Java 15 from AdoptOpenJDK PPA.

wget -qO - https://adoptopenjdk.jfrog.io/adoptopenjdk/api/gpg/key/public | sudo apt-key add -
sudo add-apt-repository --yes https://adoptopenjdk.jfrog.io/adoptopenjdk/deb/

Then you can install Java 15 with:

sudo apt-get install adoptopenjdk-15-hotspot

For more information / options / troubleshooting : https://adoptopenjdk.net/index.html

openjdk-15-jdk is available from the default repositories in Ubuntu 20.10 (and later releases). You can install openjdk-15-jdk from the Ubuntu 20.10 universe repository in Ubuntu 18.04 using apt pinning. You can also install openjdk-15-jdk without apt pinning by installing Ubuntu 20.10 in a virtual machine like a KVM/QEMU (qemu-kvm) virtual machine created in Virtual Machine Manager (virt-manager).