Unfortunately you cannot skip the r11->12.0 and 12.0->14.0 upgrades as there are significant changes to the Data-Dictionary structure (and other system databases) that must be applied during the upgrade processes. In fact most older sites have had to apply several additional remedial actions in order to complete the r11-> 12.0 -> 14.0 upgrades.
While you cannot download Datacom/DB 12.0 directly from CA Support Online, and there is no support for r11 or 12.0 environments, you will find that CA Support are a friendly bunch and will be pleased to encourage your upgrade to a current release, including supplying you with a tape image for 12.0.
The good news is that once you reach 14.0, the upgrade process has been hugely simplified, and from there you can upgrade directly from 14.0 to 15.1 (skipping 15.0 if you wish).
If you are not familiar with these upgrade processes, and would rather have the upgrades completed for you, then CA Services and several other partners are available to assist you.