For various reasons, including the compliance of the material, it can bet difficult to get the same kind of dimensional accuracy in Elastic resin as with other Formlabs resins.
https://support.formlabs.com/s/article/Using-Elastic-Resin?language=en_US if you haven’t already.
In contrast with other resins, Elastic does seem to print slightly larger than specified in the model/mesh, and this may be a combination of how the resin cures, and with the resin absorbing some IPA during the washing process and swelling as a result. For example, another user on these forums today is reporting their parts are about 1% larger than expected.
If you’re going to be printing blood vessels (like tubes) from Elastic, then your test parts should probably be cylindrical tubes with your normal wall thickness, not solid cylinders.
1.5mm walls are not too thin for elastic, but the thinner the part, the higher your surface-area-to-volume ratio is, and the more likely that IPA absorption in the wash will give you distortion problems. If you run into that kind of issue, you can try washing for a shorter amount of time and/or letting your parts dry out longer after washing before post-curing,