Due to your request to lower the prices as much as possible

[Joj]

Due to your request to lower the prices as much as possible, we have come up with a discount of approximately 15 percent off the final price for the installation of the entire PV system.
Please note that the brand that we present in our offer is of high quality additionally to the continuously monitoring system from our side after sales.

 

[emsr2d2]

In response to your request for us to lower the price, we can offer you a 15% discount on the cost of installation.

(I wouldn't bother with the rest of it. You don't have to justify your prices. You've offered them a discount. Leave it at that.)