How to reproduce:
1. Open attached project
2. Build "TextMeshUI" scene to Android device with latest 2018.3 version
3. Launch the application, observe the frame time (measurement done with three 10 second long intervals, first 5 seconds skipped)
4. Build application with some earlier version of Unity

Result --> Dynamically changing UI Text takes more frame time on newer versions of Unity

Reproducible with - 2018.3.0a4 (96052d777ea1), 2018.3.0a1 (7734a451d298)
Not reproducible with - 2018.3.0a1 (d2fa186e6a95), 2018.2.0b11 (912020d71ebf), 2018.2.0b10 (4bc57476174c)

DUT:
Reproducible with:
Google Pixel C, OS:8.1.0, CPU:arm64-v8a, GPU:NVIDIA Tegra
Google Nexus 6P, OS:8.0.0, CPU:arm64-v8a, GPU:Adreno (TM) 430
Google Nexus 6, OS:7.1.1, CPU:armeabi-v7a, GPU:Adreno (TM) 420
Razer Phone, OS:7.1.1, CPU:arm64-v8a, GPU:Adreno (TM) 540
Lge LG H815 (G4), OS:6.0, CPU:arm64-v8a, GPU:Adreno (TM) 418

Not reproducible with:
Samsung SM N950F*, OS:7.1.1, CPU:arm64-v8a, GPU:Mali-G71