update changelog for #3862 (#3869)

* update changelog for #3862

* reword

CHANGELOG.md

@@ -16,6 +16,10 @@
 - Updated `plot_voltage_components.py` to support both `Simulation` and `Solution` objects. Added new methods in both `Simulation` and `Solution` classes for allow the syntax `simulation.plot_voltage_components` and `solution.plot_voltage_components`. Updated `test_plot_voltage_components.py` to reflect these changes ([#3723](https://github.com/pybamm-team/PyBaMM/pull/3723)).
 - The SEI thickness decreased at some intervals when the 'electron-migration limited' model was used. It has been corrected ([#3622](https://github.com/pybamm-team/PyBaMM/pull/3622))
 
+## Optimizations
+
+- Sped up initialization of a `ProcessedVariable` by making the internal `xarray.DataArray` initialization lazy (only gets created if interpolation is needed) ([#3862](https://github.com/pybamm-team/PyBaMM/pull/3862))
+
 ## Breaking changes
 
 - Renamed "have_optional_dependency" to "import_optional_dependency" ([#3866](https://github.com/pybamm-team/PyBaMM/pull/3866))