Answer
Wa `alaykum as-Salamu wa rahmatullahi wa barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
1- Usury (riba) is impermissible (haram) either in housing or any other dealings.
2- As for the kind of contract you mentioned in your question, it is obviously riba (unlawful interest).
In his response to your question, Prof. Dr. Monzer Kahf, Professor of Islamic Finance and Economics at Qatar Faculty of Islamic Studies, states:
It is apparent that the difference in this example between the total paid and the sale price (15000+192000-100000=107000) is riba.
Riba is haram whether for housing or for any other purpose.
Ethiopia is a country with a large Muslim community. You should be able to amend this contract or to have the finance done through the Islamic bank.
There is a new Islamic bank in Ethiopia. To amend it, it is permissible to negotiate with the government bank to sell the house for 207000 with 15000 cash and the remainder on 800 a month. The difference is not simply formality. It is in fact a basic difference between sale on credit and interest on lending. Sale on credit is permissible and interest on loan is not.
Almighty Allah knows best.