Having a bootable driver update that contains everything your server needs is the way to go.
(Updated = We are now able to allow the full download of the ISO file. So there is only ONE file to download now.)

=-=-=-=-=-=-=-=-=>R415_bootable.iso«<=-=-=-=-=-=-=-=-=

Next, use [Rufus«] to create a bootable USB drive.
Set the following options.
[Device]: USB Drive
[Boot Selection]: R415_bootable.iso
Load the ISO into Rofus and
[Partition scheme]: MBR
[Target System]: BIOS or UEFI
[File System]: Fat32
[Cluster Size]: 4096 Bytes

(Information may vary for your server. This is the basic for the R-Series Boot Options.)
Next, boot your [R415 Server] with the USB drive in the front slot.
Press [F11] to boot into the Boot Manager.
Choose [C Drive]
Then choose the [USB Front Panel]
Do not press any keys after this. Allow the installation to do its thing.

Issues you may encounter and what to do.
(This seems to be an issue with all Dell R Series servers that have the iDrac Express card installed.
The Question mark indicates the Version Number.)
#1: Device: iDrac?
Application: iDrac?
Failed to update to standby image.

This issue will happen if the iDrac? Express card is no longer functioning.
Replacing the iDrac? Express card is required.

Dell Drivers Download Page
R-415 Drivers Page«

The man behind all the ISOs
Allen Sampsell«