You can of course keep Ubuntu 12.04LTS until 2017 but upgrades are only possible from 6-month release to 6-month release or from LTS release to LTS release. So from 12.04 LTS you can only upgrade to 12.10 or 14.04 LTS.
You could thus go from 12.04 to 14.04 to 16.04 to 16.10 to 17.04. It would probably be a bit of a hassle. (Also I don't see how you can have 1,500 beans and still ask that question...)
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