Remark: the split is easy to analyze if 10h16 and laika have the same elements on the respective two pages. (I assume they do)

Question: If we switch to two forms (like on 10h16), is it correct to assume that to get the percentage of people who donated (or "got through the process successfully") is the two submission rates multiplied?
(so if -payment form has 70% submission rate and -address form has 85% submission rate, the percentage of people who "got through the process successfully" is 0.7*0.85=0.59 → 59%)

@Jan_Dittrich In banner tests users won't usually see laika-payment because they are directed to laika-personal-data and old analysis of 10h16 indicate that only a very smalll percentage of people change sum, interval or payment provider after they came to the landing page. So, I would use the submit oder conversion rate of laika-personal-data to measure the performance of the skin.
It would be different if it is for instance an emailing test where users are direced to the first page of the form. This way your calculation should seems sensible. But I'am not sure if the submit button on 10h16_payment actually works because at the moment there are zero submits since the beginning of the test.