I do not have the RF 15-30mm...
However, I agree with one of the above recommendations. You might want to consider the EF 16-35mm f/4L IS USM and an EF to RF adapter.
There are pluses and minuses to this.
At comparable apertures, to me the EF 16-35mm looks a bit sharper with somewhat less chromatic aberration than the RF 15-30mm.
https://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=1624&Camera=1508&Sample=0&FLI=0&API=2&LensComp=949&CameraComp=979&SampleComp=0&FLIComp=0&APIComp=2 (Note: The slightly higher resolution 5DS-R used to make the test shots with the 16-35mm is probably more demanding of that lens, than the 45MP R5 used for test shots with the 15-30mm.)
The 16-35mm is an L-series lens, which is likely better built. And it has USM focus drive, which may be better than the 15-30's STM.
Further, the EF 16-35mm offers f/4 aperture throughout it's range, where the 15-30mm has a bit slower f/4.5-6.3 variable aperture.
As with most (all?) Canon L-series, the lens hood is included with the EF 16-35mm. It's sold separately with the 15-30mm.
The 15-30mm is smaller and lighter weight. It weighs under 1 lb. (13 oz.), while the 16-35mm is about 1.5 lb. (22 oz.) plus the EF to RF adapter.
The 15-30mm is smaller diameter, using a 67mm filter, while the 16-35mm uses 77mm.
The 16-35mm itself is about one inch longer than the 15-30mm, and adding the adapter to the EF lens makes it nearly another inch longer.
And, yeah, the EF 16-35mm f/4L will cost a bit more.
The RF 15-30mm is selling for $550 plus $59 (or 44£ or 50€) for the difficult to find, separately sold EW-73E hood (3rd party hoods may be avail. for less).
You can buy used copies of the EF 16-35mm in great condition for around $700 (with caps & hood):
https://www.mpb.com/en-us/product/canon-ef-16-35mm-f-4-l-is-usm?page=4 and if you don't already have one, you'll need an EF to RF adapter to use this lens on an R-series camera. There are a number of those available now:
https://www.bhphotovideo.com/c/search?q=EF%20to%20RF%20adapter&filters=fct_accelerator-booster-turbo-hidden_6898%3Ano%2Cfct_camera-body-mount_1595%3Acanon-eos-rf%2Cfct_category%3Alens_adapters_3420 Note: If you want, this is an opportunity to add a control ring (which neither lens has, though the RF lens can be switched so it's focus ring acts as a control ring). Or you could add an adapter that accepts filters.
Full review of EF 16-35mm:
https://www.the-digital-picture.com/Reviews/Canon-EF-16-35mm-f-4-L-IS-USM-Lens.aspxFull review of RF 15-30mm:
https://www.the-digital-picture.com/Reviews/Canon-RF-15-30mm-F4-5-6-3-IS-STM-Lens.aspxIn the end, if you want as small and light as possible, the RF 15-30mm might be ideal. But if you want better build, a little bit larger lens aperture and slightly better image quality, the EF 16-35mm may be a better choice.