kfw 115 or not - what do you think?

To wrap it up: we will not do KfW115, but rather stick to individual measures. So no external insulation.

With gas heating, it is difficult to achieve the KfW 115 standard..

That's not true at all. It always depends on the circumstances. I achieve KfW 85 with an oil-condensing boiler, even with pellets I wouldn't reach KfW 55. while others do manage that very well.....

You can forget about your energy consultant. You should change him.
You can reach KFW 115 even without insulation measures on the facade.
If you are already renovating, I would also rethink your financing. KFW offers credit up to 100,000 euros at 0.75% interest via program 151, with a 12.5% repayment grant.
So you would only need 50,000 euros in bank loans. Even at the Commerzbank, the interest rate is higher at 0.99%. The fixed interest period is the same (10 years), so you would definitely finance more cheaply. Regarding the 115, here’s a tip. Have an independent expert calculate the savings that an air heat pump would bring.

If you install roof insulation, new windows, and maybe a floor heating system instead of a condensing boiler, the air heat pump reduces your primary energy demand by more kWh than the condensing boiler and solar thermal combined. Above all, don’t let the consultant tell you which products you have to install. You can save quite a bit of money.
Unfortunately, I have no space on my property for an air heat pump.

KFW also does not prescribe which manufacturers you should use; they only care about the values of primary energy savings.
The calculation programs of the consultants only include the best-known manufacturers.
My solar thermal system comes from Austria Email and costs half as much as Paradigma. It achieves an equally good value at half the price and ranked fourth best in the test, which was only marginal compared to the “Porsche” of solar thermal systems.
With floor heating, you also save money if you use, for example, a dry screed system or flowing screed system. Selfio offers floor heating systems for self-installation.
They help with the planning, provide you with an offer, and also create the necessary hydraulic balancing for the consultant.

For my 102 sqm, I paid around 4500 euros complete with dry screed.
For replacing a radiator with a valve, you have to expect at least 500 euros per radiator (including installation). I have 7 radiators that need to be replaced, and the cost estimate was around 6500 with VAT.
You can have a technician do the connection and pressure testing. You only need the specialist contractor declaration for KFW, which your trusted company that also supervises the proper installation will surely provide.