Tracking Down Plan Cache Clearing
on SQL2014 SP1 changing sp_configure parameters seemed to solve problem :

sp_configure 'show advanced options', 1;
GO
RECONFIGURE;
GO
exec sp_configure 'access check cache bucket count',512;
exec sp_configure 'access check cache quota',2048;
GO
RECONFIGURE;
GO
sp_configure 'show advanced options', 0;
GO