Improve Bottleneck Performance in ASP.NET [core] System

We are developing a System based on both ASP.NET and ASP.NET Core 3.1. Recently, when doing improvements based on Load Tests, we discovered an API-Endpoint which handles both File-Uploads and some JSON Payload (it is a multipart request).

While it isn't surprising that this endpoint is the bottleneck, I think there is some room for improvement.

Hot Path

The critical path appears to be the File-Upload Management. Up to 25 Files can be uploaded (our load test send one 2MB File since this is the average).

The endpoint takes the IFormFiles, and assigns its Stream-Contents to a byte[] property of a DTO which then gets sent to another service based on .NET (not core) because it needs thje SharePoint SDK which does not support .NET Core :(.

Said service reads the byte[] into a Stream which gets sent to SharePoint where the documents are finally stored.

My Question

I guess (no clue tbh) that the RequestIFormFile.Streambyte[]StreamSharePoint chain could be realized without the conversion to and from byte[].

Is this possible and if so: would it improve the performance of the overall operation? In other words: is it possible to stream contents of an IFormFile through another Request to an intermediate WebService? (and would that make sense)