CVA reliability and validity measure

Current survey length is quite long and am trying my best to lower the drop rate of my respondents.

For measuring reliability and validity, would these options seem okay?

Repeat 1 CVA profile for reliability test

Adding 3 holdout sets for validity test as out of sample

I am a bit concerned about these numbers.

I have 5 attributes and a total of 13 levels.

I am providing 15 scenarios (1.5 times more than the parameters) and 3 choice holdouts and 1 repeat scenario.

Would I need to increase the number of holdouts and repeat scenarios?

I haven't collected the data yet.

Thank you for your help.

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