Wealth tax is quite low here (at the moment), there is no capital gains tax for personal investments (with some exceptions like direct investment in real estate) and if your investments are not yielding a large income, there will be a correspondingly low income tax.
You should declare assets/income because these are used together with your Swiss earnings etc.to calculate your tax rate in Switzerland, which is dependent on your world wide income, even if not all that income is subject to tax here. It is, of course, even theoretically possible that these push you above the 120K threshold for tax at source. See point 13 in the document below: https://www.stadt-zuerich.ch/content...t_qst14_en.pdf
As for the technicalities of bringing your investments here, I'm not sure that tax here will be the main consideration. There may, however, be some tax implications where the assets are based (withholding tax, CGT etc).
Simply ask the Bank that you have chosen to use here what they recommend/charge. If the total assets involved are relatively small, it may be better just to sell there, and buy here, in the normal cycle of reviewing your portfolio.