Problem in 12V-1A and 5V-1A Dual Supply AC/DC SMPS

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There in an instability in 12-1A output of SMPS.
With AC input 230V, +5V – 1A output was stable whereas the +12V – 1A output was not stable in NO LOAD condition.
In Load Condition where
Load = 12V – 600mA DC Motor was used as load.
+15V – 1A dropped drastically with load voltage dropping to +8.8V, whereas +5V – 1A output was stable in those load condition

Every thing was designed as per PI integration suit simulation, but still I face such problem.
Is there any mistake in my design ?
Could you suggest any better design/schematic with transformer constructional details using (TNY Switch III) especially using (TNY280PN).

Hi Sriram,

Could you please help me to understand the missed connection between the schematics and transformer diagram from your attachment?
In particular how the schematics has two outputs, secondary in AC stack on core EE25 and the transformer construction shows single output 5V, 2 strands on EE16.

Best Regards