I enter Thailand first by plane for four days. Then i will go to Cambodja/Vietnam/Loas en will come back at Thailand by crossing the border between Loas and Thailand. My question is, is it possible to get an visa for more than 15 days at the border between Loas and Thailand? If not, is there an other option for me to get an visa for Thailand in stead of arrange it from the Netherlands?

You can apply for a tourist visa in Laos, or extend your 15 day visa exempt entry (so your second entry) with 30 days at an immigration office in Thailand.

You can apply for a tourist visa at the embassy in Vientiane or at the consulate in Savannakhet. Both will issue a 2 entry visa.

You could also get a tourist visa while your are in Cambodia or Vietnam.

You can now extend a 15 day visa exempt entry for 30 days at immigration.

You could get a double entry tourist visa in your home country before you come. The validity will normally be 6 months. You use the first entry for your four day stay and activate the second entry when you come back by land from Laos. It will only work if the second entry is made on or before the "must enter by" date on the visa.

You could get a double entry tourist visa in your home country before you come. The validity will normally be 6 months. You use the first entry for your four day stay and activate the second entry when you come back by land from Laos. It will only work if the second entry is made on or before the "must enter by" date on the visa.

From the OP: "in stead of arrange it from the Netherlands"

So the OP has expressed an alternative from your solution. Agree with you though that this 'apply for a double entry visa in Amsterdam or Den Haag' would be the easiest option.