So 1.5% + 0.15% stamp duty + stocks exchange fees probably another 0.2% = 1.85% to buy ETF units. This is huge. Pure rip off.
If you decided to go for Postfinance, you can try to invest less frequent and use up trading credits. Like slightly below 5000 CHF at once.
You can also check FlowBank, their pricing looks interesting. But both Swissquote and FlowBank have custody fees, and with FlowBank the minimum is smaller. You can generate trading credits for Swissquote by using their credit card, the virtual one is free. CornerTrader have no custody fees, but you have to make at least one transaction per trimester.
And then there are German banks acting as brokers.
Good luck.