I have always found Poser rather slow at object deletion... My impression is that it kind of reload a certain number of things...
There's a free tool you could try: Snarlygribbly's Scene Fixer. You will find it in the Poser 11 section here. It contains many tools, among them the ability to delete characters, lights, props, etc...

𝒫𝒽𝓎𝓁

---

(っ◔◡◔)っ

👿 Win11 on i9-13900K@5GHz, 64GB, RoG Strix B760F Gamng, Asus Tuf Gaming RTX 4070 OC Edition, 1 TB SSD, 6+4+8TB HD
👿 Mac Mini M2, Sequoia 15.2, 16GB, 500GB SSD
👿 Nas 10TB
👿 Poser 13 and soon 14 ❤️