After the release is before the release. So engines for 15.2 are on already. It builds, passes openQA and even released the first iso image to download.opensuse.org¹ last week.
As usual you can find the sources in openSUSE:Leap:15.2 in OBS². The project is in a very early stage so it's not much more than 15.1 + updates yet.
15.2 again will be a service pack like update in the 15 series of Leap. As such by default packages will *not* be updated to Factory versions automatically and it's discouraged to drop packages.
The core packages will be inherited automatically from SLE15SP2 that also started development recently. From what we know already we will get version updates for the Kernel, GNOME and Qt from SLE.
If you think a package you take care of needs to be updated, please check whether the package is inherited from Factory or SLE. If it's from Factory submit manually once to let the tools know to follow Factory. If the package is from SLE please file a bug report and/or get in touch with the maintainer on SLE side ASAP. Updates for packages coming from SLE need to be evaluated this year still to have a chance.
Note that despite some version updates in core components we do not aim at providing the latest and greatest of everything in Leap 15. So no batch updates please!